Optimizing front-end performance: tips and methods to reduce redraws and reflows

Improve front-end performance: Tips and methods to avoid redrawing and reflow

In front-end development, optimizing performance is an important topic. Among them, avoiding unnecessary redraw (Repaint) and reflow (Reflow) operations is the key to improving page performance. This article will introduce some techniques and methods that can help developers avoid redrawing and reflowing, and give specific code examples.

1. What is redrawing and reflow

1. Redrawing: When the style of a DOM element changes, but does not affect its geometric properties (such as position and size), the browser A redraw operation will be performed. Redrawing refers to updating the visual effect of an element without affecting the layout.
2. Reflow: When the geometric properties of a DOM element change, the browser needs to recalculate the geometric properties of the element and re-layout the page. This process is called reflow.

Redrawing and reflow will cause certain performance consumption. If they occur frequently, it will seriously affect the performance of the page.

2. Tips and methods to avoid redrawing and reflow

1. Use class instead of style: When setting the element style, try to use class to modify the element's style instead of directly operating it The style attribute of the element. Because modifying the style attribute will cause a reflow operation, using class to modify the style will only trigger a redraw.

Sample code:

// 不推荐的写法
element.style.width = '200px';
element.style.height = '100px';
element.style.backgroundColor = 'red';

// 推荐的写法
element.classList.add('custom-style');

2. Use document fragment (DocumentFragment): When adding a large number of DOM elements to the page, you can first add these elements to the document fragment, Then insert the document at once, which can reduce the number of reflows.

Sample code:

const fragment = document.createDocumentFragment();

for (let i = 0; i < 1000; i++) {
  const div = document.createElement('div');
  div.innerHTML = 'Element ' + i;
  fragment.appendChild(div);
}

document.getElementById('container').appendChild(fragment);

3. Use transform instead of top/left: When you need to change the position of an element, try to use the transform attribute instead of directly modifying top and left left attribute. Because using transform will not trigger a reflow operation, directly modifying the top and left properties will cause the browser to recalculate the layout of the element.

Sample code:

// 不推荐的写法
element.style.top = '100px';
element.style.left = '200px';

// 推荐的写法
element.style.transform = 'translate(200px, 100px)';

4. Use virtual DOM (Virtual DOM): Virtual DOM is an in-memory data structure, by comparing the difference between virtual DOM and real DOM , minimizing page redraw and reflow operations. Using some popular front-end frameworks (such as React, Vue) will automatically help you operate virtual DOM.

Sample code:

// 使用 React 创建虚拟 DOM
const element = <div>Hello, World!</div>;

// 将虚拟 DOM 导入真实 DOM
ReactDOM.render(element, document.getElementById('root'));

Summary:

Redrawing and reflow are issues that require special attention in front-end performance optimization. By using class instead of style, using document fragments, using transform instead of top/left, and using virtual DOM and other techniques and methods, we can significantly reduce page redraw and reflow operations and improve page performance. In actual development, it is recommended that developers always pay attention to the performance of the page and follow the above tips and methods for optimization.

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